[Spaceships] Pool as a fuel tank

[adimar]

I'm currently designing a small luxury space yacht for a high ranking executive.
The engine design uses water as fuel, and one of the cool features that came to mind is using one of the fuel tanks as a swimming pool (Not really an original, i think this was written from one of the space odyssey books)
My intent is that the pool will be a standard fuel tank (with some minor internal customizations) and when half the fuel was used it would be used as a pool.
How would you stat this, in terms of fuel capacity?

Here is the design for reference purposes.
Peregrine space yacht (TL10, SM6)
This is a winged, streamlined design.
Capable of both atmospheric flight and excellent space performance.
And best of all is quite cheap to operate since it uses water as it's reaction mass.
A perfect craft for the busy executive or a crack team of operatives.
0.12g , 72mps, 30 tons of water.

Front
1) Adv. Metalic laminate
2-5) Habitat (Passengers: 1 Luxury cabin, 2x Standard cabins)
6,Core) Fuel tank (Water, doubles as a swimming pool)
The entire front section is mounted on an axis an spins to create artificial gravity.

Middle
1) Adv. Metalic laminate
2-5) Fuel tank (Water)
6) Control room
Rear
1) Adv. Metalic laminate
2-5) Fusion rocket (High thrust, Water: 0.03 per engine)
6) Engine room.
Core) Habitat (Crew: 1 Bunkroom)

[Flyndaran]

Maybe cut the fuel tank usability to that of a hanger bay with similar reasons of infrastructure.

[munin]

A half-empty SM+6 Fuel Tank is holding only 2.5 tons of water (625 gallons) -- that's roughly a large hot tub, not a pool. Three to five full Fuel Tanks (about 4.5 cubic meters of water each) might give you enough water for a small pool or a 25-meter lap lane.

I would probably represent this as one or more Reconfigurable Systems that can switch between being a Fuel Tank and an Establishment (a half-size establishment holds 10 people -- about right for a large hot tub).

[RyanW]

Just wanted to point out, most steam systems (almost definitely including rockets using water as reaction mass) need very pure water. Swimming pools are going to have chemicals and gunk from swimmers that will likely cause problems in the engine.

[IrishRover]

The Honor Harrington series did this, though it was actually a pool, justified by it being able to be used as fuel.

If your ship uses fusion power, purifying the water is relatively trivial--all distilling it takes is energy, and you have LOTS of that.

[Celti]

Originally Posted by IrishRover

The Honor Harrington series did this, though it was actually a pool, justified by it being able to be used as fuel.

It wasn't fuel; rather, it was drinking water storage.

Originally Posted by The Short Victorious War, Chapter 7

Most spacers were perfectly happy "swimming" in a null-gee tank, but Honor preferred water, and Nike's designers, in a burst of no doubt misplaced zeal, had provided a pool for the admiral's use. The water in it formed part of the battlecruiser's consumables storage system, which probably explained how the architect had convinced BuShips to buy it, and it was on the small side, but it was deep enough for diving.

[wellspring]

The honeymoon special in World of Ptavvs did this.

How is the ship able to enter orbit with only .12g acceleration? I know it has wings, but that just doesn't seem to be enough.

[RogerBW]

Originally Posted by wellspring

How is the ship able to enter orbit with only .12g acceleration? I know it has wings, but that just doesn't seem to be enough.

Spaceships abstracts away the detail, but basically you just keep flying higher and faster - greater speed gives you a bit more lift so that you can fly into thinner atmosphere, thinner atmosphere lets you get greater speed - until you're effectively in the zero-pressure manoeuvre régime. There probably should be a minimum thrust to do this trick effectively... otherwise it just takes too long and you run out of fuel.

[adimar]

Originally Posted by wellspring

How is the ship able to enter orbit with only .12g acceleration? I know it has wings, but that just doesn't seem to be enough.

According to wikipedia (Thrust-to-weight_ratio) the Concorde has a thrust to weight ratio of approx .3 so .12 does sound flight capable.
That being said. I would welcome some input about the minimum thrust/weight ratio that allows any level of flight and the extra propelent used by less than optimal thrust levels.

Adi